Electromagnetic switch

ABSTRACT

In an electromagnetic switch assembly having a solenoid and a movable armature attractable to the solenoid by a first electromagnetic force, improved control of armature movement is achieved including maintaining the armature away from the solenoid until a predetermined current condition exists and then causing the armature to move with improved rapid motion, that is with snap action, by applying a second force in the form of a magnetic bias to the armature in a direction opposing or negating a portion of the first force maintaining the armature away from the solenoid until the predetermined current condition comes into existence at which point the ratio of the first force to the second force changes to reverse the direction of the resultant force to allow the armature to move to the solenoid with the first force increasing as the second force is decreasing with armature movement. A second embodiment uses the first and second forces to avoid nuisance tripping upon momentary overloads by utilizing the position of a movable core within the solenoid. In a first position, the second force, tending to maintain the armature away from the solenoid, is significantly higher than the first force even upon an overload while in a second position the first force, tending to attract the armature to the solenoid, is significantly higher than the second force.

United States Patent 1 1 Grenier et al.

11 3,740,650 1 June 19,1973

[ ELECTROMAGNETIC SWITCH [75] Inventors: Aime J. Grenier, NorthAttleboro;

Richard E. Suter, Norton; Lawrence E. Cooper, Attleboro, all of Mass.

[73] Assignee: Texas Instruments Incorporated,

' Dallas, Tex

1221 Filed; Apr. 19, 1971 21 A .N6.;134,997-

[52] US. Cl. 335/239, 335/242 Primary ExaminerGeorge Harris Att0rneyI-Iarold Levine, Edward J. Connors, John A. I-Iaug, James P.McAndrews and Gerald B. Epstein 514 76/1 MiM/VASN Qfis IIIIIIIIIIIIII[57] ABSTRACT In an electromagnetic switch assembly hav-ing a solenoidand a movable armature attractable to the solenoid by a firstelectromagnetic force, improved control of armature movement is achievedincluding maintaining the armature away from the solenoid until apredetermined current condition exists and then causing the armature tomove with improved rapid motion, that is with snap action, by applying asecond force in the form of a magnetic bias to the armature in adirection opposing or negating a portion of the first force maintainingthe armature away from the solenoid until the predetermined currentcondition comes into existence at which point the ratio of the firstforce to the second force changes to reverse the direction of theresultant force to allow the armature to move to the solenoid with thefirst force increasing as the second force is decreasing with armaturemovement.

significantly higher than the second force.

8 Claims, 4 Drawing Figures v I [lire/26ers:

by Aim J. Grem'er Ric/20rd E. Safer Lawrence E. Cooper may PATENTED Jul1 sun-112mg n u 1w nu n n tal GE WJMW I i M ARL W ELECTROMAGNETIC SWITCHThis invention relates to electromagnetic switches, and with regard tocertain more specific features to flux path defining means forcontrolling the movement of an armature of a device for opening orclosing a circuit.

Among the several objects of this invention may be noted the provisionof means to improve the characteristic of armature movement to obtainimproved rapid or snap action movement of the armature toward thesolenoid of the device to effect concomitant opening or closing of acircuit. Another object of the invention is the provision of anelectromagnetic switch which is insensitive to overloads of shortdurations. Yet another object is the provision of suchapparatus which isreliable yet relatively inexpensive, apparatus which is readilycalibrated, has few moving parts to maximize longevity and apparatuswhich can be used with essentially any electromagnetic device having amovable armature. Another object of this invention is the provision of anew and improved magnetic circuit breaker assembly for the protection ofelectrical circuits and components against sustained overloads and shortcircuits especially one in which the flux generated is efficiently usedboth to actuate the circuit breaker and to obviate nuisance tripping.Other objects and features will be in part apparent and in part pointedout hereinafter. I

The invention accordingly comprises the elements and combinations ofelements, steps and sequence of steps, features of construction andmanipulation, and arrangements of parts, all of which will beexemplified in the structures and methods hereinafter described, and thescope of the'application of which will be indicated in the appendedclaims.

In the accompanying drawings in which several of the various embodimentsof the invention are illustrated:

FIG. 1 is an elevational view, partly in cross section and partlyschematic-of'one of the various possible embodiments of the'invention;

I picted in FIG. 2 and showing forcesacting upon it.

Corresponding reference characters indicate corresponding partsthroughout the two views of the drawings.

Dimensions of certain of the parts as shown in the drawings may havebeenmodified or exaggerated for the purposes of clarity of illustration.

Conventionally an electromagnetic switch has an armature movable towardand away from a solenoid to actuate some type of switch mechanism.Spring means is normally used to bias the armature into a first positionremoved from the armature when there is either no current orinsufficient current in the solenoid to attract the armature to thesecond position contiguous to the solenoid. This spring may be adjusted,for example, to maintain the armature in the first position even with acertain current, or predetermined level, passing through the solenoidthus offsetting the electromagnetic force on the armature caused by thepassage of current through the solenoid. When the current exceeds thepredetermined level the electromagnetic force on the armature exceedsthe spring force and thus the armature begins to move toward thesolenoid against the bias of the spring. This bias of the spring,however, still acts on the armature and militates against its movementtoward the solenoid thereby tending to slow its movement. It is possibleto offset this characteristic to some extent by employing a springhaving a decreasing rate, that is, a spring which exerts decreasing biasor force on the armature as it moves toward the solenoid. However, thisdoes not completely solve the problem since it is desirable to providevibration insensitivity for the device. In order to avoid the situationof having a sudden force applied to the armature in a direction tendingto move the armature toward the solenoid, which might happen if thedevice were suddenly jarred, and not having sufficient bias left in thespring to overcome this jarring force along with any existingelectromagnetic force a reasonably large safety factor must be factoredinto the spring, thus resulting in slower motion of the armature upon anoverload. The present invention results in improved snap actingcharacteristics of the armature by applying a second force to thearmature which biases the armature away from the solenoid at the sametime the usual first electromagnetic force is applied to the armaturebiasing the armature toward the solenoid. The second force can beadjusted so that the spring need not be employed. That is, the secondforce can be made greater than the first keeping the armature away fromthe solenoid until a certain current level is achieved in the solenoidat which point the resultant of the forces is reversed with the firstforce becoming greater than the second and the armature is thenattracted to the solenoid. As the armature moves toward the solenoid,the second force on the armature rapidly decreases while the first forceconcomitantly rapidly increases. In some instances it may be desirableto use a relatively small spring bias just to maintain the armature awayfrom the solenoid when in the deactuated condition. Inthis case, as wellas in the case of not employing a spring, the second force is sufficientto prevent movement of the armature toward the solenoid upon vibrations.

As seen in FIG. 1, a device 10 comprises flux producing means in theform of a solenoid 12 preferably wound on a nonmagnetic bobbin 14. Asolid core 16 of magnetic material such as steel is telescopicallyreceived within the solenoid and is provided with a pole piece 18 on oneend and is attached at the other end thereof to a magnetic path definingframe member generally indicated as 20. Frame 20 is formed into a firstmagnetic path P, comprising pole piece 18, core 16, bottom portion 22contiguous with an end of the solenoid, upstanding member 24, air gap B,armature 26 contiguous to member 24, air gap C and back to pole piece18. Frame 20 is also formed into a second magnetic path P comprisingpole piece 18, core 16, a generally U-shaped portion of frame 20comprising a leg or bottom portion 22, bight portion 28 and top leg 30,gap D, distal armature portion 32, air gap C, and back to pole piece 18.Means 34 for altering the reluctance of magnetic path P is shownschematically in bight portion 28. This may take the form of aconstricted section of bight portion 28, a switch changing an air gap,forming all or a portion of the frame 22 lying within P of materialwhich magnetically saturates before P or any other conventional meansfor altering the reluctance of a member. The total reluctance of path I:may be calibrated or adjusted by placing a layer 36 of nonmagneticmaterial on distal portion 32 of the armature and also by forming dimple38 in top member 30. Provision of layer 36 also avoids the possibilityof armature 26 sticking to top leg 30 and provides more consistentoperation over the life of the breaker by reducing the effect of wear-inor small foreign particles collecting at the contact point. The radiusof dimple 38 not only affects the reluctance of path P but also affectsthe magnitude of F obtained for a given flux level in path P byaffecting the flux patterns and distribution in gap D between the dimpleand the top of armature 26. Dimple 38 further provides more consistentoperation since the area of contact of a flat surface mating with arounded surface is more predictable than two mating flat surfaces. Itshould be noted that it may be desirable in some instances to round offthe top surface of pole 18 for the same reason.

It will be seen that the U-shaped portion of frame 20 encompassessolenoid 12 and distal armature portion 32. Armature 26 is pivotablymounted at 40 and movable from a first position in contact with top leg30, shown in FIG. 1 in solid lines, to a second position in contact withpole piece .18, shown in dashed lines, and vice versa. Movement ofarmature 26 actuates a switch mechanism shown schematically at 42through any convenient linkage arrangement as suggested by dashed line44. Armature 26 is normally biased into the position shown in solidlines in the nonactuated condition either through the linkage mechanism44 or by a separate spring, for instance a spring located at pivot 40.This bias is preferably'just enough to cause the armature to move towardtop member 30.

Operation of device is explained as follows. When electric current flowsthrough solenoid 12 an electromagnetic field is established with fluxconcentrated in pathsP, and P The reluctances of the paths can beadjusted so that the force F see FIG. 1a, occasioned by normalcurrentflow applied to armature 26 through path P, tending to attract thearmature toward pole piece 18 less the bias of a spring, if one isemployed, is less than the force F FIG. 1a, applied to armature 26through path P tending to attract the armature toward top member 30 sothat the armature, remains in the solid line position. As the currentincreases in the solenoid, the flux in path P increases proportionately.The increase of flux in path P however, is limited by means 34, forinstance by saturation of a portion of leg 28, so that upon sufficientincrease in current flow through solenoid 12 force F 1 becomes largerthan force F and thus the armature 26 is attracted to pole piece 18. Assoon as armature 26 begins to move the reluctance of gap D markedlyincreases while the reluctance of gap C decreases reversing theresultant of forces, F sharply increasing while opposing force F, issharply decreasing resulting in snap-acting motion of armature 26. Thispositive, fast motion of the armature permits a more precise andaccurate calibration of the device, that is, of actuating switchmechanism 42 at the same time of making available a high force fortransmission through linkage 44.

Another problem which is commonly associated with electromagneticswitches, particularly when they are used as circuit breakers, is thatof nuisance tripping of the device. This refers to interruption of acircuit upon occurrence of a high overload of duration sufficientlyshort that it is not detrimental to the particular load being protected.An example of a common type of momentary overload is the occurrence ofhigh amplitude transients of relatively short duration occasioned by theswitching on an electric power supply. It is desirable in such instancesto provide some means to prevent tripping of such a circuit breakeruntil the overload exists for some predetermined interval of timerelated to the specific amount of overload. A typical electromagneticcircuit breaker is provided with a time delay mechanism such as adashpot mechanism in which a core moves through a fluid-filled dashpotchamber. The desired time delay is obtained by retarding movement of thecore through the fluid chamber. When the core approaches the pole piecethe flux density is increased sufficiently to attract the armature andcause it to pivot toward the pole piece thus tripping the breaker.However, this type of time delay mechanism may not prevent tripping dueto the high amplitude transients mentioned above which occur when apower supply is switched on, even through the inrush lasts for a periodof time less than that required for movement of the core to the polepiece. The magnitude of this type of overload is sufficiently largeto-substantially instantaneously attract the armature of the circuitbreakers operating mechanism thereby tripping the breaker andfrustrating the function of the time delay.

Various attempts have been made to prevent this type of nuisancetripping including the provision of shunt paths in which a portion ofthe flux developed by the solenoid is shunted away from the armature.Such schemes however are inherently inefficient since a significantportion of the flux produced is shunted away from the armature and is ineffect, wasted and results in a device which is less sensitive tosustain overloads and has less force available for desired tripping.Further, such devices frequently require additional moving parts for theshunt mechanism adding to the expense of the apparatus and introducingmaintenance and reliability problems. i

The embodiment of the present invention depicted in FIG. 2 eliminatesthe nuisance tripping problem yet obviates the disadvantage of the priorart. In this embodiment flux producing means in the form of solenoid 12,similar to that shown in FIG. 1, is wound about bobbin 14; however,instead of the solid core used in FIG. 1 a dashpot mechanism comprisinga thin-walled elongate tube preferably of brass or other suitablenonmagnetic material, closed at its upper end by a cover or cap 18secured to the tube, is telescopically received within solenoid 12.Cover 18 is magnetizable and constitutes a pole piece of a circuitbreaker, relay or the like. The lower end of the tube 102 is closed byany conventional stopper means or formed integrally with the side wallsas indicated in the Figure, as by drawing. An elongate armature core 104located in tube 100 is shorter than the tube and movable axiallytherein. Core 104 is made of iron, steel or other suitable magnetizablematerial.

A hydraulic fluid or other suitable fluid maybe inserted and fillsubstantially the portion of tube 100 not occupied by core 104. Thefluid is forced from one end of the tube to the other around theperiphery of the core when core 104 is moved in the tube. Passage aroundthe periphery constitutes a restriction which limits the rate of fluidflow from one end of tube 100 to the other end thereof, therebyretarding the rate of movement of the core 104 and providing a desiredtime delay for sustained overloads. It will be understood that a fluidpassage can be provided by other means, such as by grooves or othershape formations in the inner surface of tube 100 or in the outersurface of core 104 or by a passage through the core.

The bottom end of tube 100 projects from the solenoid and the core isbiased against closed end 102 (the position shown in the drawings) by areturn coil spring (preferably nonmagnetic) which reacts from the innersurface of cover 18 against the upper end of core 104. Spring 106 iskeptaxially aligned in tube 100 by stub 108 on core 104.

Passage of current through solenoid l2 creates a magnetic field in adaround the solenoid and within tube 100 which attracts core 104 towardthe upper portion of tube 100 and into a central portion of thesolenoid. When the core 104v reaches a central portion of the solenoid,the reluctance of the magnetic circuit is reduced due to the presence ofthe magnetizable core and there is a resulting increase in the strengthof the magnetic field initially created by passing current through thesolenoid. This increase in the magnetic field attracts armature 26 and.is used to operate a v free portion 32adapted to move toward and awayfrom pole piece 18.

A' second bracket 120 of magnetizable material is generally U-shaped andencompasses frame 1 10, armature 26 and solenoid 12. Frame 120 has afirst leg 122 located on the side of the armature portion 32 removedfrom thesolenoid and is preferably provided with a dimple 38 as in theFIG. '1 embodiment. Shim 36 is also shown on the face of armatureportion 32 which comes into engagement with dimple 38. A second leg 124is spacedfrom the bottom'of the solenoid and interposed supportingmember 112 by a cylindrical spacer 126 of nonmagnetic material. Leg 124is provided with aperture 128 which receives the bottom portion of tube100. In order to minimize the reluctance between leg 124 and core. 104 asleeve 130 of magnetic material may beplaced about tube 100 in contactwith leg 124.

Magnetic path P comprises pole piece 18, gap E, core104, gap F betweenthe core and leg 112, frame 110, gap H, armature 26 and gap I back topole piece 18. Another magnetic path comprises a pole piece 18, gap E,core 104, gap .1 between core and leg 124 when the-core is located atthe bottom of the tube as shown or gap J from the bottom of the core 104and leg 124 when in the raised or actuated position (indicated by dashedline 132 bracket 120, gap-K including shim occurs (magnitude andduration of the overload being inversely proportional). As explainedabove when the core moves to a central position in the solenoid, theelectromagnetic force on the armature F see FIG. 2a, tending to attractit to the pole piece becomes strong enough to cause the armature topivot to the dashed line position. This in turn causes the circuitbreaker 42 to trip or break the circuit through linkage 44. However uponmomentary overloads, that is overloads which last for a period of timeless than that required for the core 104 to move upwardly, the flux inpath P, is concentrated due to the low reluctance between the core andleg 124 when the core is in the position shown and is greater than theflux path P Thus a force F,, FIG. 2a, is applied to armature portion 32attracting it to dimple 38 and away from pole piece 18. This results ina ratio of forces acting upon the armature such that on momentaryoverloads a resultant force attracts the armature to the full lineposition shown. The higher the overload,-when the relationships of thecomponents are optimized, the greater this resultant force keeping thearmature away from the pole piece (i.e. F F, F However, when the coremoves into the solenoid (the bottom surface of the core indicated bydashed line 1 32) the resultant force is reversed. A large reluctance(gap J) is added to magnetic path P, largely eliminating force Fnandforce F due to the lower reluctance of diminished gap E with the core inthe upper position has increased. The resultant force on the armaturepor tion 32 (F F;, F, with F, negligible) attracts the armature towardthe pole piece 18 and causes it to pivot to the dashed line position.The sudden change in the ratio of forces results in a sudden snap actingtype movement of the armature. This movement is enhanced since nearlyall of the flux produced by the current in the solenoid is used toattract the armature to the pole piece, yet no moving parts are added tothe device to increasethe cost or decrease longevity and reliability.

Thus it will be seen that by providing flux path P, momentary overloadsactually increase the force maintaining the armature away from thesolenoid thereby completely obviating nuisance tripping. Further, thisis accomplished with no additional moving parts and in such a way thatthe flux generated in the solenoid is efficiently utilized. That is, allthe working flux passes through the armature to either maintain it awayfrom the solenoid or to cause it to move toward the solenoid to causetripping of the breaker.

As many changes could be made in the above constructions withoutdeparture from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings, shall be interpreted as illustrative and not in a limitingsense, and it is also intended that the appended claims shall cover allsuch equivalent variations as come within the true spirit and scope ofthe invention.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practiced or carried out in variousways. Also, it is to be understood that the phraseology or terminologyemployed herein is for the purpose of description and not of limitation.

We claim:

1. An electromagnetic switch comprising a solenoid having first andsecond ends,

a pivotably mounted armature having an end adapted to move toward andaway from the first end of the solenoid,

first flux path means including a member of low magnetic reluctancehaving a first end contiguous with the second end of the solenoid, themember having a second end contiguous with the armature,

second flux path means including a generally U- shaped element of lowmagnetic reluctance, the U- shaped element having first and second legsjoined by a bight portion, the first and second legs having distal endportions, the distal end portions of the first and second legs mountedadjacent respective first and second ends of the solenoid, a portion ofthe armature being intermediate the first end of the solenoid and thedistal end portion of the first leg and the first end of the first fluxpath member being intermediate the second end of the solenoid and thedistal end portion of the second leg and time delay means to preventactuation of the switch upon a sustainedoverload until passage of apredetermined time interval, the time delay including a hollow elongatetubularelement of nonmagnetic material having two ends telescopicallyreceived within the solenoid and extending outwardly from the second endof the solenoid and an elongate core of magnetic material shorter thanthe tubular element slidablyv received within the tubular element andadapted to slide from one end of the tubular element to the other endthereof.

2. A switch according to claim 1 in which hydraulic fluid is placed inthe tubular element to retard movement of the core, and a spring isplaced in the tubular element to bias the core toward an end thereof.

3. A switch according to claim 1 in which the first end of the firstflux path member and the distal end portion of the second leg areseparated by a nonmagnetic spacer, the position of the core in thetubular element affecting the magnetic reluctance between the second endof the solenoid and the distal portion of the second leg, when the coreis at one end of the tubular element a relatively large reluctanceexists between the second end of the solenoid and the distal portion ofthe second leg while a relatively small reluctance exists when the coreis at the other end of the tubular element.

4. A switch according to claim l in which a shim of high reluctancematerial is located on the distal end portion of the first leg and isadapted to be engaged by a portion of the armature.

5. A switch according to claim 1 further including a switch mechanismwhich is actuated upon sufficient movement of the armature.

6. A switch according to claim 1 in which an aperture is defined in thefirst end of the first flux path member and an aperture is defined inthe second leg of U- shaped element, the cylindrical element beingreceived in the two apertures.

7. A switch according to claim 6 in which a bushing of low reluctancematerial is received about the periphery of an end of thecylindricalelement and is in contact with the secondleg of the U-shapedmember.

8. An electromagnetic switch comprising flux producing means including asolenoid having first and second ends,

a pivotably mounted armature having an end adapted to move toward andaway from the first end of the solenoid,

first flux path means including a member of low magnetic reluctancehaving a first end contiguous with the second end of the solenoid, themember having a second end contiguous with the armature,

second flux path means including a generally U- shaped element of lowmagnetic reluctance, the U- shaped element having first and second legsjoined by. a bight portion, the distal end portions of the first andsecond legs encompassing the solenoid and the said end of the armatureadapted to move toward and away from the solenoid, and time delay meansto prevent actuation of the switch upona sustained overload untilpassage of a predetermined time interval, the time delay means includinga movable core of low magnetic reluctance and means for slidinglymounting the core within the solenoid, the core movable into and out ofthe second flux path.

1. An electromagnetic switch comprising a solenoid having first andsecond ends, a pivotably mounted armature having an end adapted to movetoward and away from the first end of the solenoid, first flux pathmeans including a member of low magnetic reluctance having a first endcontiguous with the second end of the solenoid, the member having asecond end contiguous with the armature, second flux path meansincluding a generally U-shaped element of low magnetic reluctance, theU-shaped element having first and second legs joined by a bight portion,the first and second legs having distal end portions, the distal endportions of the first and second legs mounted adjacent respective firstand second ends of the solenoid, a portion of the armature beingintermediate the first end of the solenoid and the distal end portion ofthe first leg and the first end of the first flux path member beingintermediate the second end of the solenoid and the distal end portionof the second leg and time delay means to prevent actuation of theswitch upon a sustained overload until passage of a predetermined timeinterval, the time delay including a hollow elongate tubular element ofnonmagnetic material having two ends telescopically received within thesolenoid and extending outwardly from the second end of the solenoid andan elongate core of magnetic material shorter than the tubular elementslidably received within the tubular element and adapted to slide fromone end of the tubular element to the other end thereof.
 2. A switchaccording to claim 1 in which hydraulic fluid is placed in the tubularelement to retard movement of the core, and a spring is placed in thetubular element to bias the core toward an end thereof.
 3. A switchaccording to claim 1 in which the first end of the first flux pathmember and the distal end portion of the second leg are separated by anonmagnetic spacer, the position of the core in the tubular elementaffecting the magnetic reluctance between the second end of the solenoidand the distal portion of the second leg, when the core is at one end ofthe tubular element a relatively large reluctance exists between thesecond end of the solenoid and the distal portion of the second legwhile a relatively small reluctance exists when the core is at the otherend of the tubular element.
 4. A switch according to claim 1 in which ashim of high reluctance material is located on the distal end portion ofthe first leg and is adapted to be engaged by a portion of the armature.5. A switch according to claim 1 further including a switch mechanismwhich is actuated upon sufficient movement of the armature.
 6. A switchaccording to claim 1 in which an aperture is defined in the first end ofthe first flux path member and an aperture is defined in the second legof U-shaped element, the cylindrical element being received in the twoapertures.
 7. A switch according to claim 6 in which a bushing of lowreluctance material is received about the periphery of an end of thecylindrical element and is in contact with the second leg of theU-shaped member.
 8. An electromagnetic switch comprising flux producingmeans including a solenoid having first and second ends, a pivotablymounted armature having an end adapted to move toward and away from thefirst end of the solenoid, first flux path means including a member oflow magnetic reluctance having a first end contiguous with the secondend of the solenoid, the member having a second end contiguous with thearmature, second flux path means including a generally U-shaped elementof low magnetic reluctance, the U-shaped element having first and secondlegs joined by a bight portion, the distal end portions of the first andsecond legs encompassing the solenoid and the said end of the armatureadapted to move toward and away from the solenoid, and time delay meansto prevent actuation of the switch upon a sustained overload untilpassage of a predetermined time interval, the time delay means includinga movable core of low magnetic reluctance and means for slidinglymounting the core within the solenoid, the core movable into and out ofthe second flux path.